The invention relates to a piston pump which is provided for use in a slip-controlled hydraulic vehicle brake system.
Piston pumps of this kind are known in and of themselves. The known piston pumps have a cylindrical piston which is guided so that it can move axially in a pump bore in a pump housing and can be driven to execute a reciprocating stroke motion by means of a cam which can be driven to rotate in particular by means of an electric motor. In the projection of the piston, a displacement chamber of the piston pump adjoins the end of the piston remote from the cam. By means of its reciprocating stroke motion, the piston alternatingly compresses and expands a volume of the displacement chamber in the pump bore, which is defined by an end face of the piston.
The known piston pumps have the disadvantage that they are large, in particular long, and as a result of this, take up a large amount of installation space.
In the piston pump according to the invention, the piston is embodied as a hollow piston and an inner chamber of the hollow piston constitutes a displacement chamber of the piston pump. The piston can, for example, be embodied as a hollow cylinder and can be embodied as closed at one end with a radial wall, in particular an end wall. The invention""s relocation of the displacement chamber inside the piston reduces the structural length of the piston pump; the piston pump is compact in structure and requires little space. In order to further shorten the structural length or further reduce the amount of space occupied by the piston pump, a valve, which controls the through flow direction of the fluid to be supplied by the piston pump, is disposed in the inner chamber of the piston. As a result, the valve does not require any space outside the piston. In particular, the valve is an inlet valve or outlet valve of the piston pump; it is preferably embodied as a springless or spring-loaded check valve. A valve seat part, which contains a valve seat of the valve, is affixed inside the piston.
In one embodiment of the invention, an intermediary space between a piston wall of the hollow piston and the valve seat part constitutes a fluid opening for allowing fluid to travel into or out of the displacement chamber. The intermediary space can be embodied to as annular by means of a smaller outer dimension of the valve seat part in comparison to an inner dimension of the hollow piston. The intermediary space can also be constituted by axial grooves in the circumference and radial grooves in an end face of the valve seat part which, together with the hollow piston, constitute fluid conduits. This embodiment of the invention permits a simple and inexpensive design of the fluid inlet or fluid outlet.
The piston pump according to the invention is particularly provided as a pump in a brake system of a vehicle and is used in the control of pressure in wheel brake cylinders. The abbreviations ABS, ASR, VDC, or EHB are used for such brake systems, depending on the type of brake system. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to supply brake fluid from a storage tank into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR, VDC, or EHB). The pump is required, for example, in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or ASR), for example, a locking of the wheels of the vehicle during a braking event when there is strong pressure on the brake pedal (ABS) and/or a spinning of the driven wheels of the vehicle when there is strong pressure on the gas pedal (ASR) can be prevented. In a brake system that serves as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the path desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies the brake fluid into the wheel brake cylinder or cylinders if an electrical brake pedal sensor detects an actuation of the brake pedal or in which the pump is used to fill a reservoir of the brake system.